The invention refers to a method and a device for automatically analyzing volatile substances in gases, in particular in air, the method comprising the following successive steps:
a) the gas to be analyzed is passed through an absorption or reaction solution, PA1 b) the solution is analyzed by a chromatography method. PA1 a) The analysis by means of the two chromatographic methods commonly in use, i.e. the high resolution liquid chromatography (HPLC) and the capillary gas chromatography (CGC) allows to inject only about 20 .mu.l or 5 .mu.l respectively of the absorption or reaction liquid into the chromatograph column. Taking into account a liquid volume of about 20 ml this represents only 1% or less of the entire sample volume and signifies a corresponding loss in sensitivity. PA1 b) The absorption or reaction recipient having a volume of several milliliter cannot be cleaned at reasonable expenditure to an extent which is necessary for a sensitive measurement. Therefore the memory effect is high. The memory effect is further increased by the duct through which after exposure the solution to be analyzed must flow towards the chromatograph. For this reason this duct must also be cleaned after each analysis cycle. Moreover the volume of the recipient cannot be reduced in size at will since the length of this duct imposes a lower limit of recipient volume. Thus, in each cycle 20 ml of solution should be pumped towards the chromatograph. Under these conditions concentrations of down to 50 ppb of formaldehyde had to be measured.
Such methods and devices are known: An article of A. Gromping and K. Cammann "Development of an automated, quasi-continuous method for the simultaneous determination of nitrogen oxides, aldehydes, and ketones in air" published in the periodical INSTRUMENTATION SCIENCE & TECHNOLOGY 22 (1994), pages 25 to 38 describes a method of this type according to which the gas to be analyzed is passed through a recipient (impinger) which is nearly completely filled with a reaction solution, the gas sparkling upwards through the solution. After the intended exposure time a part of the solution is pumped via ducts and by means of a peristaltic pump into a chromatograph while the remaining solution is withdrawn from the recipient. The latter is then cleaned and charged with fresh solution for the next analysis cycle. All these steps are automatically supervised and controlled by a sequential program.
A main inconvenience of this method is the low sensitivity especially due to the following effects:
The increasing pollution burden of closed rooms due to the improvements in the thermal isolation and the use of poisonous adhesives in the furniture industry and for posing wallpapers or carpets has created a need for a low cost measurement and supervision of even lower pollutant concentrations, especially the concentration of formaldehyde in the concentration range below 50 ppb.